update with no changes

Why this happens ?

create table t(i int);
CREATE TABLE
insert into t values(1);
INSERT 0 1
select (ctid::text::point)[1]::int, * from t;
 ctid | i
------+---
    1 | 1
(1 row)
update t set i = i;
UPDATE 1
select (ctid::text::point)[1]::int, * from t;
 ctid | i
------+---
    2 | 1
(1 row)

If nothing was changed, why create a new record, append data to wal, set old record as deleted, etc, etc ?

regards,

Marcos